The present invention relates generally to building construction. More particularly, the invention concerns a device and framing system for use in supporting a supplemental roof in superposed spaced relation to the primary roof of a building so that insulation may be provided on the exterior side of the primary roof.
Plank, post, and beam building systems have been used for many years in the construction of roof structures. Since these so-called "deck roofs" provide an exposed ceiling of planks and beams, which when finished, is aesthetically pleasing, they have heretofore been widely popular with consumers.
In addition to providing aesthetic benefits, planked roof construction was also very popular for many years because of the low labor costs associated with its installation.
As energy costs have escalated significantly, the provision of adequate insulation for the roof of a building has become a paramount concern. For new construction, local building codes almost universally require that minimum standards of insulation be met. Where such codes are in force, post-and-beam plank roof construction has been virtually eliminated for residential roof construction. This significant decline in deck roofing has occurred because of the difficulties associated with adequately and economically insulating this type of roof. Since homeowners are interested in preserving the appearance of the plank ceiling, insulating on the underside of the roof is a workable, but not desirable, option. The only option then has been to provide the insulation on the outer side of the roof. According to one approach, sheets of rigid insulation are nailed in place directly on the planks that form the deck roof. Thereafter, layers of building paper and shingles are placed atop the insulation. Since there is no airspace between the rigid insulation and roofing material, there are serious condensation problems with this approach. As well, to obtain a satisfactory amount of insulating effect, the sheets of rigid insulation must be thick, e.g., approximately three inches to obtain an R30 insulating value. As a result, conventional roofing nails cannot be used and resort must be had to large spikes that may penetrate completely through the roofing planks and be visible on the ceiling. To avoid these problems, another prior approach has been to construct a second roof over the deck roof using large rafters or a truss structure. While these arrangements enable the placement of insulating batts or blankets between the rafters or trusses, they do so by significantly increasing the cost of construction, both in terms of material and labor.
In the known approaches that utilize a rafter arrangement, two-by-twelve framing materials are typically chosen in an effort to maximize the thickness of insulating material. As a general rule, two-by-twelve materials are the largest framing members that are readily available in a lumber yard. In actuality, the net dimensions of the two-by-twelves are 11/2 inches by 111/4 inches. Twelve-inch-thick blankets of insulation, which yield an insulating value of R38, cannot be easily fitted into a void created by using two-by-twelve materials. It will be appreciated that even if this were possible, it would not be desirable since there would be no remaining airspace between the insulation and the supplemental roof. The omission of a space for air movement has critical import, both in the context of heating loads and cooling loads. Without adequate airspace in the heating situation, condensation occurs, wetting the insulation. In hotter climates, where air conditioning rather than heating is a concern, a large air void is required to exhaust heated air below the roof so that it does not enter the home or building. Under these circumstances, an even larger air void is necessary.
In view of these concerns, smaller blankets of insulation, such as those 8 to 81/2 inches thick, which yield about an R30 insulating value, must be used with two-by-twelve rafters. In cold areas in particular, this is an insufficient amount of insulation. To achieve higher values of insulation, it is accordingly necessary to resort to the extremely costly option of a flat truss structure. The same option must be chosen in those areas where the air conditioning load is the principal concern. In these areas, a large airspace rather than a heavy blanket of insulation is more important for cooling. In general, a two-by-twelve rafter does not yield a desirable space that would provide the correct combination of insulation thickness and air gap.
A solid two-by-twelve rafter construction for a supplemental roof suffers from another disadvantage. Even if the thicknesses of insulation and airspace might be adequate for a milder climate, the arrangements of rafters spanning the space between the supplemental and primary roof restricts air movement to a direction from eave to ridge in the spaces between adjacent rafters. Greater effectiveness in the removal of warm air for cooling purposes and less likelihood of condensation in heating situations would occur if it were possible to enable air movement from gable end to gable end of a building in addition to movement from eave to ridge.
There still remain a substantial number of older residences and buildings that have uninsulated deck roofs. If the owners of these buildings are interested in insulating the roofs, they are faced with the choices presented to the new building contractor. Thus, they must choose among destroying the aesthetics of the cathedral ceiling by insulating on the underside of the roof, opting for only marginally effective rigid insulation, or expending considerable sums to build a second roof with rafters or trusses. As noted above, rafter construction yields less than desirable insulating results in many situations.
The present invention provides an arrangement that overcomes the disadvantages of the developments described above. In particular, the invention provides a device and framing system that can be used to easily and economically support a supplemental roof above a primary roof of a building. Since the device and system are readily adapted to provide a number of different spacings between the supplemental and primary roof, the invention enables insulating the outer surface of the primary roof to equal or exceed the R-value mandated or suggested by building codes for new construction and remodeling. While the invention is particularly suited for use with deck roofs, it is also useful as a means for insulating both new and old truss roofs having pitches too low to provide enough room for adequate ceiling insulation and airspace above the insulation.
Of particular advantage is the invention's enablement of the use of smaller framing materials, i.e., two-by-four and two-by-six members, in lieu of a two-by-twelve rafter to provide the support for a supplemental roof. These smaller framing members not only cost significantly less than their larger counterparts, but are much easier to handle so that they may be lifted to the roof and cut to proper size. As a result of this ease of use, labor costs are also favorably impacted so that the overall cost of the supplemental roof is kept low. Unlike the solid rafter approaches that block the movement of air in a crosswise direction, the inventive arrangement yields an open space above the insulation through which air may circulate in any direction. The invention is particularly concerned with ensuring that the thickness of insulation as well as the airspace above it are complementary to one another and adapted to optimize either heating or cooling requirements.